Icing of power transmission lines caused by low temperature and rain or snow constitutes one of serious threats to power systems in a lot of countries. Severe icing will cause large-area power outage due to grid disconnection and tower collapse. It also leads to difficulties to resume power supply. The threat of ice disaster is always one technical difficulty fought by the industry of power systems for a long time.
In 1998, storm in North America had a serious effect on power grids in America and Canada, which caused large-area power outage. In 2005, low temperature and rain or snow caused large damage to Central China and North China Power Grids. In January-February, 2008, low temperature and rain or snow attacked south China, central China, and east China, which caused large-area and long-term outage of power transmission lines in Guizhou province, Hunan province, Guangdong province, Yunnan province, Guangxi province, Jiangxi province, and so on and further caused enormous losses to national economy and people's livelihood.
Many deicing/ice melting techniques were researched in industrial circles and academic circles to reduce the serious threat of more frequent ice disaster to the infrastructures of power systems. Wherein, the basic principle of direct current ice melting is as follows: alternating current electric power available from the power system is converted into direct current electric power by high-power rectifier devices, then the direct current electric power is input to wires of lines to be subjected to ice melting, the wires are heated with the action of the direct current to ensure that the ice covered thereon is melted, and therefore, the risks of line disconnection and tower collapse are eliminated. The direct current ice melting technique overcomes the limitation of alternating current ice melting, and inductive components of line resistance do not function during direct current ice melting, which greatly reduces the volume necessary for direct current ice melting and increases the ice melting efficiency. Further, during direct current ice melting, the direct current voltage is continuously adjustable, ice melting requirements of lines with different lengths may be met through adjusting the direct current output voltage, and no impedance matching is needed, thus the strict demand on operation modes of the power system is greatly lowered. Moreover, a direct current ice melting device located in a load-center substation may be used to melt ice covered on all the lines through the substation.
In the world, the former Soviet Union started using diode rectifier devices to melt ice since 1972, and later adopted silicon controlled rectifier devices. The direct current research institute of Russia successfully developed silicon controlled rectifier ice melting devices of two voltage classes: 14 kV (powered by a 11 kV alternating current bus) and 50 kV (powered by a 38.5 kV alternating current bus). The rated power of the 14 kV device is 14 MW, and the rated power of the 50 kV device is 50 MW. The 50 MW device was put into operation in a substation in 1994, and successfully applied to deicing of a 110 kV power transmission line of 315 km. After ice disaster in North America in 1998, the Quebec Electricity And Water Authority and the AREVAT&D company invested 25 millions EUR to cooperatively develop a direct current ice melting device, and one set of direct current ice melting device was mounted in the Lvis substation of the Quebec power grid, with the volume of 250 MW and the direct current output voltage of ±17.4 kV, and its design purpose is to melt ice covered on four 735 kV lines and two 315 kV lines. This device was subjected to field test in 2008, but so far has not been implemented in practical ice melting.
After ice disaster in 2008, power scientific and technical workers in China autonomously performed research and development of the direct current ice melting technique, and successfully researched and developed high-power direct current ice melting devices possessing completely independent intellectual property rights, mainly including many models such as a model with special rectifier transformers, a model with no special rectifier transformers, and a vehicle-mounted movable model, and further they were popularized and applied across the China, so far about 20 sets of direct current ice melting devices in total have been put into operation, where 19 sets of direct current ice melting devices have been provided in the China Southern Power Grid.
In January, 2009, the Guizhou Power Grid Corporation performed direct current ice melting on a 500 kV FuShi II line, a 220 kV FuJiu line, a 110 kV FuNiu line, and a 110 kV Shuishumei line, the Yunnan Power Grid Corporation performed direct current ice melting on a 220 kV ZhaoDa I line, and the Guangdong Power Grid Corporation performed direct current ice melting on a 110 kV TongMei line. In November, 2009, the Yunnan Power Grid Corporation performed direct current ice melting on a 110 kV DaZhong T line. Initial practical applications indicate that the direct current ice melting technique is an effective means of deicing the power grids.
In January, 2011, large-area icing attacked the China Southern Power Grid again, 19 sets of direct current ice melting devices which have been installed in the China Southern Power Grid all played a major role, and performed 217 times of direct current ice melting in total on the lines of above 110 kV, where more than 40 times of direct current ice melting on alternating current lines of 500 kV, which fully played a role of the direct current ice melting devices.
In view of the practical application effect of the direct current ice melting devices, the power grid enterprises in China started a new round of large-scale popularization and application since 2011 again.
However, it is found that in the practical application in the icing periods from 2009 to 2011, the existing direct current ice melting devices needs to be optimized in some aspects. For example, in one aspect, a saturable reactor of a converter has a large noise. In another aspect, current interruption occurs during short line ice melting. In a further aspect, the current-through test can only be done when the ice melting device is switched in the power transmission line, which is limited by the operation mode of power grids and also affects its normal operation.